Generally, liquid crystal displays (LCDs) are primarily used for display devices such as notebook computers, desktop computers, and TVs due to advantages of implementing a lightweight and compact design and low power consumption. However, since an LCD is not a device which spontaneously emits light by itself but a light-receiving device, a backlight unit is required in addition to a liquid crystal screen.
FIG. 1 is a schematic cross-sectional view of an LCD according to a related art.
Referring to FIG. 1, the LCD 1 according to the related art includes a liquid crystal panel 10, a backlight unit 20, a cover bottom 30, a guide panel 40, and a top case 50.
The liquid crystal panel 10 includes a thin film transistor substrate 12 and a color filter substrate 14 bonded to each other with a liquid crystal layer interposed between. Also, polarizing members 16 and 18 may be respectively attached to a lower surface and an upper surface of the liquid crystal panel 10. Also, the backlight unit 20 includes a reflection sheet 21, a light source 23 configured to provide light to the liquid crystal panel 10, a light-guide plate 25, a plurality of optical sheets 27, and a housing 29 configured to support the light source 23.
The cover bottom 30 includes a receiving space therein to receive the light source 23, the reflection sheet 21, the light-guide plate 25, and the optical sheets 27, and simultaneously supports the guide panel 40. The guide panel 40 is designed to support the liquid crystal panel 10. As illustrated in FIG. 1, the guide panel 40 may include a panel support portion configured to support the liquid crystal panel 10 and sidewalls surrounding the backlight unit 20. The top case 50 covers not only the edges of the upper surface of the liquid crystal panel 10 but also the side surfaces of the guide panel 40 and the cover bottom 30.
Here, the light-guide plate 25 directs light from the light source 23 toward the liquid crystal panel 10. The light-guide plate 25 primarily includes a polymer material such as poly methyl methacrylate (PMMA) or poly carbonate (PC). The light-guide plate 25 is a key component of the backlight unit 20 to produce a plane light source by uniformly distributing, in an upper direction, light from the lateral light source 23 while minimizing a loss of the light.
However, PMMA, etc., which are materials primarily used for the light-guide plate 25 in the related art, have disadvantages that shapes thereof are deformed and harmful volatile organic compound, etc. are generated at high temperature (90° C.). Also, a coefficient of thermal expansion (CTE) is about 50 to 100×10−6/K, which is high, and thus there is a limit in reducing a width of a bezel part, which is a non-display area of the liquid crystal panel 10. Furthermore, since PMMA is a polymer material and so has low mechanical strength, the guide panel 40, which is a metal frame, is additionally used to reinforce the low mechanical strength. Also, PMMA requires a thickness of about 3.5 mm in order to provide optical characteristics inside the backlight unit 20, which limits a slim profile of the LCD 1.
Therefore, a light-guide plate having high-temperature stability, that is, which is not deformed even when exposed to a high temperature environment, which does not generate a harmful gas while it is used, which has a low CTE, which has high mechanical strength and thus does not require a metal frame, etc., and which is advantageous in manufacturing a slim profile display device, and a manufacturing technology thereof are required.
Currently, examination of a new product that applies glass as a material of a light-guide plate is in active progress. Generally, compared with a polymer material according to a related art, glass has excellent mechanical physical properties and thermal durability, but has high light absorption due to a characteristic of a material itself and so it is difficult to uniformly transfer light from a backlight unit to an entire area without color change.
Particularly, reduction of a color difference in a glass light-guide plate is an urgent issue. As described with reference to FIG. 1, in the light-guide plate, the light source is located at a lateral side of the light-guide plate and light propagates. In this case, a difference between color of a portion close to the light source and color of a portion away from the light source occurs due to a light-absorption component inside the light-guide plate, which is referred to as a color difference. In the glass light-guide plate, the color difference tends to seriously appear compared with a polymer light-guide plate according to a related art.